Bradykinin (BK) is a linear nonapeptide produced endogenously in humans and other mammals as a result of the activity of kallikreins, a group of proteolytic enzymes present in most tissues and body fluids, on kininogens. Once released, kinins produce many physiological responses, including pain and hyperalgesia by stimulating C- and A-fibers in the periphery. There is also considerable evidence that kinins contribute to the inflammatory response.
Native Bradykinin has the amino acid structure described on page 127 of Burch et al., (DuPont Biotech Update, 1992:4:127-140) and numerous other references.
Bradykinin, and its physiologically important related peptides kallidin (Lys-bradykinin) and Met-Lys-bradykinin, exhibit physiological actions which qualify them as mediators of inflammatory reactions, hypotensive states, and pain. Bradykinin is overproduced in pathological conditions such as septic shock, anaphylaxis, rhinitis, asthma, inflammatory bowel disease, and certain other conditions including acute pancreatitis, post-gastrectomy dumping syndrome, carcinoid syndrome, migraine, and angioneurotic edema. The production of bradykinin from the plasma results in pain at the site of the pathological condition, and the overproduction intensifies the pain directly or via bradykinin-induced activation of the arachidonic acid pathway which produces prostaglandins and leukotrienes, the more distal and actual mediators of inflammation.
In addition to its proinflammatory effects, bradykinin is a vasodilator. Because of its concomitant ability to lower blood pressure, bradykinin has been implicated in the pathogenesis of several shock syndromes, particularly septic or endotoxic shock. Bradykinin is also a potent bronchoconstrictor in animals and asthmatic subjects and it has been implicated as a contributor to the pathogenesis of airway inflammatory conditions such as allergic asthma and rhinitis.
As a result of the implication that increased levels of bradykinin may play a part in a number of pathological conditions, considerable research has been aimed toward the derivation of bradykinin receptor antagonists as potential therapeutic agents. A bradykinin receptor antagonist is expected to possess a number of desirable biological effects in the treatment, for example, of pain and inflammation, septic shock, airway disorders such as asthma, burn pain, pancreatitis, angioedema, certain nervous system disorders, chronic inflammation such as rheumatoid arthritis and inflammatory bowel disease, rhinitis, and allergy.
Several non-peptide, non-specific and non-selective antagonists of one or more of the biological activities of bradykinin have been described among compounds as diverse as analgesics and anti-inflammatory substances, which act via the prostaglandin system and not directly on bradykinin receptors. These are antihistamines, bradykinin-antibodies, benzodiazepine derivatives, high molecular weight ethylene oxide polymers, gallic acid esters, and serotonin inhibitors. None of these compounds or classes of compounds specifically inhibit the effects of bradykinin.
Heptyl esters of various amino acid-containing substances, such as single basic amino acids the dipeptide Phe-Gly, and analogs of C-terminal peptide fragments of bradykinin (i.e., Pro-Phe-Arg) have been reported as anti-bradykinin substances. When tested in bradykinin assay systems, they prove to be weak partial agonists/antagonists, depending on the dose, with little specificity for inhibiting bradykinin action.
Several research groups have prepared bradykinin receptor antagonists. The first antagonists of bradykinin were discovered by Stewart and Vavrek. U.S. Pat. Nos. 4,801,613 and 4,693,993 (which references are incorporated in their entirety herein) disclose a series of bradykinin antagonists wherein the L-Pro at the 7-position of the peptide hormone bradykinin or other substituted analogs of bradykinin is substituted with an aromatic amino acid of the D-configuration which converts bradykinin agonists into bradykinin antagonists. The specific L-Pro substitutions are selected from the group consisting of D-Nal, D-PNF, D-Phe, D-Tyr, D-Pal, D-OMT, D-Thi, D-Ala, D-Trp, D-His, D-Homo-Phe, D-Phe, pCl-D-Phe (CDF), D-Phg, D-Val, D-Ile, D-Leu, and MDY. Typically, these bradykinin antagonist peptides had K.sub.i values in the range of 20-80 nM in guinea pig ileum (Stewart, J. M., et al., In Bradykinin Antagonists (1991) Burch, R. M., Marcel Dekker, New York).
Subsequently, several classes of bradykinin antagonist peptides with 600-1000-fold greater potency in the guinea pig ileum preparation have been disclosed. Published European Patent Application No. 0 413 277 A1 to Hoechst A. G. discloses bradykinin antagonists containing the aromatic amino acid D-Phe at position 7 but containing unnatural amino acids at position 8 which impart increased potency.
Published European Patent Application No. 0 370 453 A2 to Hoechst A. G. discloses bradykinin antagonists containing a D-imino acid (D-Tic) at position 7.
A more recent series of bradykinin receptor antagonist peptides lacks the D-aromatic amino acid at position 7 which was believed to be critical to the activity of the earlier described antagonists of the endogenous neuropeptide. As described in published PCT application WO 92/18156 and WO 92/18155 (which references are incorporated in their entirety herein) this group of compounds have a general bradykinin antagonist structure wherein the L-Pro at position 7 is substituted with hydroxyproline ether and thioether derivatives (termed D-Hype) and the L-Phe at position 8 can additionally be substituted with hydroxyproline ethers and thioethers derivatives (Hype), Tic or Oic.
The bradykinin antagonist peptides referred to above exert their activity by blocking the bradykinin B.sub.2 receptor. A second bradykinin receptor, the B.sub.1 receptor, is not expressed to any significant degree in healthy tissue, but its expression is upregulated during persistent inflammatory hyperalgesia. This receptor is activated by des Arg.sup.9 -kalladin and des Arg.sup.9 -bradykinin, a proteolytic degradation product of bradykinin. It is believed to play an important role in the maintenance of hyperalgesia in chronic inflammatory conditions (Dray, A. and Perkins, M., TINS, Vol. 16, No. 3 (1993) 99-103). [Des-Arg.sup.9 ] analogs of bradykinin B.sub.2 receptor antagonist peptides of the type described above bind to the B.sub.1 receptor and have been shown to reverse or prevent hyperalgesia in animal models of persistent inflammatory hyperalgesia, whereas the corresponding B.sub.2 receptor antagonists were ineffective or weakly active in these models (Perkins, M et al., Pain, 53, (1993) 191-197).
One limitation of the bradykinin antagonist peptides known to date is the necessity for parenteral administration. Due to the peptidic nature of the compounds, they are unlikely to be orally active. Further, peptides in general tend to have a relatively short duration of action as a consequence of their rapid matabolic degradation. As a result, non-peptide or pseudopeptide bradykinin receptor antagonists that lack the limitations of a peptide offer meaningful therapeutic advantages.